Fundamental Technology Research LNG Propulsion System

About LNG Propulsion System

The LNG Propulsion System, a new technology using liquid oxygen and liquefied natural gas

The "LNG propulsion system" is a new propellant system to gain thrust by burning liquid natural gas (LNG whose major content is liquid methane) and liquid oxygen in a rocket engine.
Its performance is at mid-level between a liquid hydrogen propulsion system and a solid rocket system, but it is characterized by many benefits such as the system can be smaller because LNG's concentration is higher than liquid oxygen. It can also be stored for a long time in space, and has good safety. Therefore, by combining with a liquid oxygen propulsion system, the LNG propulsion system can make it possible to construct a space transportation system that can freely cope with various space activities for the future

Characteristics of LNG Propulsion System

Liquid rocket engine

A liquid-fueled launch vehicle is propelled by burning liquid fuel mixed with oxidizer. The performance and character of a launch vehicle vary depending on the combination of the types of oxidizer and liquid fuel. Some typical examples of the combination are liquid oxygen/liquid hydrogen, liquid oxygen/kerosene, and dinitrogen tetroxide/hydrazine.
In the case of the second stage engine, the LE-5B-2, and the first stage engine, the LE-7A, for the H-IIA Launch Vehicle, liquid oxygen is used as an oxidizer, and liquid hydrogen for fuel ("Hydrogen propulsion system.") The advantages of the above combination are clean emission and a high performance. However, due to the lower density of hydrogen, more volume is required, thus a hydrogen tank becomes bulky.

Benefits of LNG propulsion system

The "LNG propulsion system", which uses a combination of liquid oxygen and liquid natural gas, has the following advantages despite lower performance.

  • It is less evaporable in space; therefore, it is suitable for a vehicle that travels to space for a prolonged period, such as an inter-orbit transporter and planetary probe.
  • Propellants are less expensive thus the launch cost can be reduced.
  • The possibility of an explosion is lower, hence it is safer.
  • Thanks to the high density, the propellant tank can be smaller; therefore it is suitable for a large-size launch vehicle such as a reusable transporter.

By taking advantage of the above merits, the LNG propulsion system has a potential to be applied for various projects including a first stage propellant system for a reusable transportation system, and an inter-orbit transporter and planetary probe that requires relatively low thrust for a moon and planetary exploration project.